In recent years various solid polymers of polypropylene have gained increasing popularity as thermoplastic molding materials for making a great variety of molded objects. Because of their unique combination of low density, high abrasion resistance, good chemical resistance, relatively high softening point and low cost, propylene polymers, particularly the crystalline propylene polymers, are good candidates for use as fiber reinforced thermoplastic compositions. Glass fiber reinforced polyolefin resins have better stiffness, impact resistance and heat resistance than unreinforced polyolefin resins. These glass fiber reinforced polyolefin resins have been broadly used for various industry parts such as automobile parts and electrical parts.
However, use of fiber reinforced polypropylene has been to some extent limited by difficulty of securely bonding the polymer matrix to the inorganic fiber. Even when polyolefins such as crystalline polypropylene are glass fiber reinforced, particularly when they are melt-kneaded together, the resulting material properties are not optimum because of poor adhesion of the matrix resin to the glass fibers. In the case of polypropylene, this is particularly a problem because of the non-polarity of polypropylene. When larger amounts of glass fibers are added to polyolefin resins, especially polypropylene, the fluidity of the polymer is lowered, making it difficult to use the fiber reinforced resins for molding applications.
It has been found that chemically modifying the crystalline polypropylene with an ethylenically unsaturated organic acid or organic acid anhydride will result in modified polypropylene from which articles having improved properties can be molded.
Silanes having both a substituent reactive with the surface of an inorganic fiber and an acid reactive with an organic matrix have been used with chemically modified polypropylene, particularly crystalline polypropylene, to enhance bonding of the matrix material to the inorganic fiber reinforcement, with resulting increases in strength of articles made from such molding compositions.
However, there is still a continuing need for glass reinforced resins from which can be molded articles having a good balance of various physical properties, mechanical properties, electrical properties and thermal properties.